UV-induced immobilization of tethered zirconocenes on H-terminated silicon surfaces

A tethered ethylenebis(indenyl) zirconocene was covalently immobilized on H-terminated Si(111) surfaces using UV-mediated alkene hydrosilylation, thus making possible the development of structured catalytic surfaces with highly controlled properties.     

Seed loading effects on the mean crystal size of acetylsalicylic acid in a continuous‐flow crystallization device

This study investigates the effects of seed loading on the mean crystal size of the model substance, acetylsalicylic acid, crystallized from ethanol in a continuously seeded tubular crystallizer. A hot, highly concentrated ethanolic acetylsalicylic acid solution was mixed with an acetylsalicylic acid‐ethanol seed suspension. Subsequent cooling of the slurry in the tubing promoted supersaturation and hence crystal growth. The tubular shape of the 15 m‐long crystallizer with an inner diameter of 2 mm enabled narrow residence time distributions of the crystals in the pipe and excellent temperature control in the radial direction and along the tubing. Crystals entering the crystallizer had both identical growth conditions in each section and about the same time for crystal growth. Narrow crystal size distributions were achieved with decreasing differences in the volume‐mean‐diameter sizes of the seed and product crystals as seed loadings increased. Decreasing the seed size had a similar effect as increasing the seed loading, since in that case the same amount of seed mass resulted in more individual seed particles. Altering the arrangement of the coiled crystallizer with respect to spatial directions (horizontal, vertical) did not lead to a significantly different outcome. All experiments produced considerably larger product crystals in comparison to the seeds despite relatively short crystallization times of less than 3 min. Moreover, product mass gains of a few hundred percent at a g/min‐scale were achieved. Similarities in product crystal samples taken at different times at the outlet of the crystallizer showed that steady‐state conditions were rapidly reached in the continuous flow crystallization device. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A two-sided Arnoldi algorithm with stopping criterion and MIMO selection procedure

In this paper we introduce a two-sided Arnoldi method for the reduction of high order linear systems and we propose useful extensions, first of all a stopping criterion to find a suitable order for the reduced model and secondly, a selection procedure to significantly improve the performance in the multi-input multi-output (MIMO) case. One application is in micro-electro-mechanical systems (MEMS). We consider a thermo-electric micro thruster model, and a comparison between the commonly used Arnoldi algorithm and the two-sided Arnoldi is performed.     

Controlled silicon surface functionalization by alkene hydrosilylation

Immobilization of indene ligands onto two types of hydrogen-terminated surfaces, oxide-free Si [H/Si(111)] and oxidized Si [H/SiO2/Si], has been investigated by infrared absorption spectroscopy. The activity of a common catalyst (H2PtCl6) is shown to depend critically on the nature of the solvent. For instance, 2-propanol preferentially reacts with the surface, preventing any ligand attachment. Chlorobenzene is more stable, allowing some ligand attachment, but the H2PtCl6 catalyst also fosters silicon oxidation. In contrast, UV irradiation on oxide-free surfaces promotes a cleaner and more efficient reaction, leading to ligand attachment without substrate oxidation. The complete inactivity of H-terminated surfaces with a thin oxide layer [H/SiO2/Si] suggests that the UV-induced immobilization is mediated solely by the excitation of electron-hole pairs (excitons) in the substrate and is not the result of direct Si-H bond breaking.     

Modeling a seeded continuous crystallizer for the production of active pharmaceutical ingredients

The approximation of a well mixed reactor is prevalent when it comes to the modeling of a crystallization process. Since temperature, concentration, and mass content vary due to inhomogeneous mixing, this approximation is a very loose one. The continuously operated seeded tubular crystallizer system developed in our group overcomes obstacles like a slow response to changes in the outer parameters and inhomogeneous mixing. Therefore the applicable well mixed assumption facilitates detailed modeling of the crystallization process by means of population balance equations (PBE) coupled with mass and energy balances. Modeled results were validated by means of experiments. The amount of aggregation events during the crystallization could be quantified and it was proven that the growth of seeded crystals is almost exclusively responsible for solid mass uptake if the reactor is operated appropriately. The performed sensitivity analysis exposed which process settings should be maintained most accurately to avoid fluctuations in the product crystals’ quality attributes and to limit undesired nucleation events.     

Working group report: Heavy-ion physics and quark-gluon plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.